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<h2><a name="SECTION0020270000000000000000">
18.2.7 Installing your CGI script on a <span class="Unix">Unix</span> system</a>
</h2>

<p>
Read the documentation for your HTTP server and check with your local
system administrator to find the directory where CGI scripts should be
installed; usually this is in a directory <span class="file">cgi-bin</span> in the server tree.

<p>
Make sure that your script is readable and executable by ``others''; the
<span class="Unix">Unix</span> file mode should be <code>0755</code> octal (use "<tt class="samp">chmod 0755
<var>filename</var></tt>").  Make sure that the first line of the script contains
<code>#!</code> starting in column 1 followed by the pathname of the Python
interpreter, for instance:

<p>
<div class="verbatim"><pre>
#!/usr/local/bin/python
</pre></div>

<p>
Make sure the Python interpreter exists and is executable by ``others''.

<p>
Make sure that any files your script needs to read or write are
readable or writable, respectively, by ``others'' -- their mode
should be <code>0644</code> for readable and <code>0666</code> for writable.  This
is because, for security reasons, the HTTP server executes your script
as user ``nobody'', without any special privileges.  It can only read
(write, execute) files that everybody can read (write, execute).  The
current directory at execution time is also different (it is usually
the server's cgi-bin directory) and the set of environment variables
is also different from what you get when you log in.  In particular, don't
count on the shell's search path for executables (<a class="envvar" id='l2h-3828' xml:id='l2h-3828'>PATH</a>) or
the Python module search path (<a class="envvar" id='l2h-3829' xml:id='l2h-3829'>PYTHONPATH</a>) to be set to
anything interesting.

<p>
If you need to load modules from a directory which is not on Python's
default module search path, you can change the path in your script,
before importing other modules.  For example:

<p>
<div class="verbatim"><pre>
import sys
sys.path.insert(0, "/usr/home/joe/lib/python")
sys.path.insert(0, "/usr/local/lib/python")
</pre></div>

<p>
(This way, the directory inserted last will be searched first!)

<p>
Instructions for non-<span class="Unix">Unix</span> systems will vary; check your HTTP server's
documentation (it will usually have a section on CGI scripts).

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<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
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